This application relates to apparatus and methods for treating article surface with liquids. More particularly, the apparatus and methods of the invention is directed to treating or coating with a liquid medium articles having complex surfaces, including, for example, both exterior and interior surfaces of heavily cored castings and/or mechanically formed, e.g. drilled or bored passages and other cavities in such castings and/or in fabricated articles.
The advantages of employing a dipping treatment of articles to be coated or otherwise treated with a liquid medium long has been recognized. Such advantages include, for example, low coating application or other liquid treating cost, amenability to bulk processing, comparative ease of applying heavy (thick) coatings of liquid, speed of film application or other surface treatment, low skill requirements, and ready coverage of "blind" surfaces.
Major problems which have been associated heretofore with dip coating and treatment processes and apparatus include excessive drag off of entrapped liquid media, slowing of otherwise available processing rate due to the time required for gravity drainage, erratic and non-uniform film thickness in coating processes, webbing of the liquid in article cavities, especially threaded holes, and incomplete surface coverage because of entrapped air in the article cavities.
The present invention provides apparatus and methods which achieve all of the advantages of dip coating and other treatment, but which avoid such problems. The invention is especially directed to the coating of articles as above described with films of paint or other coating media. The invention as herein described is applicable, however, to any type of liquid treatment under ambient conditions of temperature and pressure and, as required, can be adapted to other than ambient conditions. A typical example of non-film-coating applications is liquid cleaning of article surfaces.
The invention is most particularly suitable for the painting of exterior and interior surfaces of articles such as cored and drilled metal castings. However, it is to be understood that, in the following description, unless otherwise indicated in a particular context, the terms "painting" and "coating" are to be construed as including application of non-paint liquid films, cleaning and like liquid surface coatings and treatments.